Heating furnace



June 3, 1930. H M, w|| |AMs y 1,761,028

v HEATING FURNACE Original Filed March 50, 1926 y grains or particles.

Y50 heat :treating-process through Patented June 3, '-1930 f UNITED STATES PATENT ol-Flcav HARRY M; WILLIAMS, DAYTONQAOHIO, ASSIGNOR TO GENERAL MOTORS RESEARCH CORPORATION, OF DETROIT, MICHIGAN, AOOBPORATION OI' DELAWARE c HEATING rUnNncE' Original application led Iaroh 80, 1926, Serial No. 98,600. Divided and this application filed November 1,' 1927. Serial No. 280,826.

This invention relates to the manufacture of porous metal articles such as shafts, bearings, or other objects which are used 1n rnb-` bing contact with relatively moving metallic.

'5 bodies. The porosity of the article is provided bya large number of minute voids or cells, which are connected by small capillary passages which render the body capable of absorbing substantial quantities of lubricant.

which is given out to the surface in contact f with the relatively moving body.

he objecty of thepresent, invention is to rovide improvements in the apparatus used 1n the manufacture of porous metal bodies, 1n

ordery to. reduce the cost of the manufacture and to improve thequality. ofthe product.

This application is a division of ap lica- 1- tion Serial Number 98,600, filed Marc 30, 1926.',; v. e Further objects and advantages of the present invention will be apparent` from the following description, reference being had to the accompanying drawings, wherein apreferred form of the ly shown.

In' the drawings: i Fi 1 is a diagrammatic, longitudinalsectional view of a eat treating. furnace used in the process of making porous metal articles according to t-he present invention.

Fig. 2 is a sectional view on the line 2--2 ofFig.lv g

The process of making porous metal bodies, to which the present-invention relates, 'consists chiefiy'in mixing finely divided metals and graphite, in briquettin'g the mixture to .form an article of the desired shape, and in heating the article insa non-oxidizing atmosphere and toa temperature suiiicient to cause 40 alloyage of the metallic ingredients. The

graphite remains inertbut spaces the particles of thealloyed metals, so that minute capillary passages are formed between the particles of graphite and v The porosity of the article is increasedby usingan organic volatile substance l'in ythe mixture of the metallic'powders and :graphite; "This substance will `'escapeduring the "ces of the present lnvention is clearparticles of the alloyedincreasing the porosity.

The following formula is typical:

Copper 90 Tin 10 Graphite r 6 Salicylic acid. 2 Ammonium chloride O. 5

.Y The proportions are Weight of the total mixture and the ingredientsare mixed into a finely, divided state. Aftermixing thoroughl; the mixture is briquetted into the desired ape under relatively high pressure, for example, 7/5,000 pounds per square inch. The

yarticles are placed in a non-oxidizing atmosphere and heated to' a temperature and for a time sufficient yto cause alloyage of the metallic particles but not to cause fusion ofthe particles into a solid mass.4 Durin the heat treating operation the copper an A tin will alloy to form grains of copper-tin alloy separated, by crystals of graphite and by Iinute cells which remainafter the escape of the volatile ingredients. It has been the practice to pack the articles vto be treated in iron or steel -pots and cover them with'charcoal or the like 1n order to protect them from the oxygen which may be present' in the heat treating furnace. After the heat treatin operation the boxes are removed from the urnace and are cooled to room temperature before theremoval of the contents. Itj-is obvious that considerable time is consumed in loading and unloading these boxesv and fthat some heat must be wasted in order to heat the boxes and the packing material as well as the ymetal articles. f

. The prsent invention provides for heating the `"b r-lquetted articles in a non-oxidizing atmosphere-which contains vCO2 land CO and v for cooling the articles gradually in a si-lilar atmosphere. In orderto'carry out this processfthe present inventionprovidcs for heating the briquettedha4 t' l clef' n a surface fcombustion furnace and for gradually cooling the article in a cooling chamber communicating with said furnace.

Referring to the drawings, numeral cooling chamber 27. The combustion products of the furnace which include inert gases, CO2 and a reducing gas such as C0, will pass into the chamber 27 and also up the stack 28. The chamber 27 is connected with the stack y 28 by flue pipe 29. Stack 28 is provided with a damper 30, and pipe 29 with adamper 31. These dampers may be regulated to vary the temperature of the chambers 21 and 27 and also quantity `of the combustion products which enter the chamber 27.

A chain conveyor 40, represented byl parallel dot and dash lines, is roved around sprocket wheels 41, 42, 43, 44 and 45. and extends along the floors of chambers 21 and 27 The sprocket 44 is the driving sprocket and is driven through a worm wheel 46, a worm 47 and a shaft 48 by a motor 49. The motor is operated so as to cause the chain to move through the furnace in the direction of arrow 50. lThe articles to be heat treated are placed in trays. 51, which are laid upon the conveyor chain.

The chain proceeds through the furnace chambers at a'wrate sufficient to produce the degree of sintering desired. The articles are heated in chamber 21 to a temperature of A about 1600o Fahrenheit which is below the fusionpoint of copper, the metallic ingredient which has the highest fusion point.

` The temperature and time are sufficient to produce alloyage of the copper and tin while the articles are inthe chamber 21. As the articles progress through the chamber 27 from the hottest part to the coldest part they are subjected to the combustion products of chamber 21 which include CO2 and CO. By the time the trays l51 have passed out of the furnace rear door 52, they will have been cooled to such a temperature that the oxygen in the external atmosphere will have no harmful effects.

After removal fromthe trays the articles are machined or swaged to thedesired Size and are impregnated with lubricating oil.

By subjecting the articles to an atmosphere which is entirelyfree of active oxygen, the temperature may be carried to a higher degree than in furnaces requiring that the articles be packed in charcoal or other similar materials.

Consequently the time of heat treatment may be materially reduced. It is believed that the carbon monoxide tends to reduce the lmetallic oxide whichv may be present and therefore facilitates the alloyage of the Inetallic particles. The carbon dioxide may 1ncrease the porosity of the material by reacting to some extent with the graphite. The desired atmosphere within the furnace may be produced by regulating the proportions of fuel and air which are admitted by the pipes 22 to the nozzles 23.

A furnace which has'been found satisfactory. for heating small articles, such as bearings for one inch shafts or smaller, is one having a chamber 21 which is 32 inches wide, 15 inches deep and 6 inches high;'and having a cooling chamber 27 provided by a pipe which is 10 feet long` and 7 inches in diameter. The diameter of Hue 28 is 4% inches; and Hue 29, 2% inches. The temperature in the chamber 21 should be preferably from 1500 to 1580 degrees Fahrenheit. The temperature in the cooling chamber 27 will vary from 1100 to 1350 degrees adjacent to chamber v21 to a temperature of from 200 to 300 degrees Fahrenheit at the rear opening 52. Gas analysis of the gases taken from different points in the furnace show that there is practically no oxygen in the chamber 21 and in the portion of chamber 27 near to the chamber 21. At a point near where the pipe 29 joins the chamber 27 the oxygen in the chamber 27 was found to be from 2% to 3% and to be between 5% and 6% near the door 52. The carbon monoxide was found to v'ary from 9% to 11% in the chamber 21 to from 3% to 4% near the rear opening 52. The carbon dioxide was found to be present in quantities of 3% to 5% in the `furnace and cooling chamber.

While the form of embodiment of the invention as herein disclosed, constitutes a preferred form, it is to be understood that other xforms might be adopted, all coming within the scope of the claims which follow.

What is claimed is as follows:

1. Apparatus for heat-treating articles composed of finely divided metals, and graphite comprising, in combination, a sintering chamber containing surface combustion means for heating said articles in the reducing atmosphere of combustion products of surface combustion, a.cooling chamber for said articles in communication'with said first chamber, an exit flue leading from said sintering chamber, a branch flue leading from said exit Hue to said cooling chamber, and

valve means in ysaid ues for maintaining a regulated amount of combustion products in said cooling chamber.

2. Apparatus forheat treating articles composed of finely divided metals and graphite, flromprising,v in combination, a chamber for receiving the combustion products of Isury.

face combustion, a non-insulated elongated cooling chamber in open communication with the first chamber, a passage connecting said chambers and adapted to conve combustion products from the first cham er into the cooling chamber, and means for conveying articles successively through said first and second chambers.

3. Apparatus for heat treating artlcles composed of flnely divided metals and gra hite, comprising, incombination, a cham er for receiving the combustion products of surface combustion, a non-insulated elongated cooling chamber in open communication with the first chamber, a passage connecting said chambers and adapted to convey combustion products from the first chamber into the cooling chamber. l

4. Apparatus for heat treating articles composed of finely divided metals and gra hite, comprising, in combination, a cham er for receiving the combustion products of' surface combustion, la non-insulated elongated cooling chamber in open communication with the first chamber, a passage connecting said chambers and adapted to convey combustion products from the first chamber into the cooling chamber, and means for regulating the flow of combustion products through said passage.

In testimony whereof I hereto affix my signature.

HARRY M. WILLIAMS. 

